Electronic computing devices, such as laptop computers, tablet computers, smart phone handsets, etc. include many different modules assembled together within the device chassis. Each module may include various integrated circuits (ICs) attached to a substrate, such as a printed circuit board (PCB). While IC chips are often permanently affixed to their substrate, for example by solder interconnects, at the module-level assembly often relies on removable fasteners, such as edge connectors and/or screws. The screws are often a metal, such as stainless steel. While metal screws are a centuries-old technique for joining components, their use within modern electronic computing devices is not without issues.
One issue is that a typical metal screw can apply high forces on an IC module, particularly if torque specifications are not followed during assembly. Over-torqueing a screw will usually damage the IC module well before the threads are stripped or the screw otherwise damaged. For example, when an assembly screw is over-driven a module PCB can be crushed between the screw head and mount. Over-tightening can also cause the PCB to deflect, stressing nearby IC solder joints toward the point of failure.
Another issue is that a typical metal screw, even if tightened to within a torque spec, does not have a low enough modulus to yield under stress associated with thermal cycling of the assembly. For example, screw elongation will typically not occur before the stress is concentrated and relieved by mechanical failures at the microscale, often at the interface of an IC and a PCB (e.g., solder joints).